This invention relates to optical communication and more particularly to a semiconductor laser module incorporating a driver circuit therein, adapted for use as a light transmitter for a high speed transmission system of the giga-bits band.
The conventional semiconductor laser modules incorporating a driver circuit therein for use in medium speed light transmission of several hundreds Mb/sec or below are described in IEEE, journal of Lightwave Technology, LT-2, No. 4 (1984) p. 398. As disclosed in this article, the connection between a semiconductor laser and an IC mounting board mounting a semiconductor laser driving IC is done by wire-bondings. The inductance of a wire used for wire-bonding is, for example in the case of using a Au wire of 25 .mu.m diameter, about 1 nH per 1 mm length. In the above-mentioned conventional art, four wires are used in parallel in order to reduce the inductance and suppress the deterioration of the modulation performance.
When a wire or wires of wire-bonding are used for the connection between the semiconductor laser and the driver IC, since the thermal resistance of the wire is high, the flow of heat generated in the driver IC into the semiconductor laser can be suppressed to a low flow. But, the inductance becomes a problem. In the prior art, the inductance is reduced by increasing the number of wires. When applied in a high speed transmission system of several hundreds Mb/sec or above and particularly the ultra-high speed transmission system of the giga-bits band, the mutual inductance among a plurality of wires and the parasitic reactance such as stray capacitance become problems and may form factors for causing deterioration of the modulation characteristics. Also, the dispersion in the wire length arising from the dispersion in the wire-bonding process also causes dispersion in the performance of the module.
The above-mentioned prior art does not take the points of the stray capacitance, the parasitic inductance, and the dispersion in the performance which become problems in the high speed transmission system and more particularly in the giga-bits band, into consideration and has problems in the high speed modulation action in the giga-bits band. Reference may be made to Nos. JP-A-62-112389, JP-A-58-119690, JP-A-5370689 and JP-A-53-68588.